This invention deals generally with electrical measuring and testing, and more specifically with the determination of the non-electric property of the state of cure of a thermosetting polymer by the use of time domain reflectometry.
The degree of cure of thermosetting polymers is of considerable interest in industry because the cure status determines the strength of a part and also whether it can be subjected to subsequent manufacturing processes. However, since the cure status of the internal portion of a part can not be evaluated visually, considerable effort has been expended to find methods to accurately evaluate the cure state.
Several electrical methods to determine cure state have been used. Among them are the measurement of impedance (U.S. Pat. No. 5,432,435 to Strong et al), reflection of continuous microwave energy (U.S. Pat. No. 5,059,914 to Lacombe et al), and dielectric properties (U.S. Pat. No. 4,777,431 to Day et al). Carrozzino et al have also performed laboratory tests (noted in Polymer Engineering And Science March 1990, Vol. 30, No. 6, pp 366) on the use of time domain reflectometry to evaluate the degree of cure. However, Carrozzino concluded that such an approach had poor accuracy and repeatability, and the publication did not disclose the use of in-situ sensors or the measurement of viscosity.